Methods to reduce debonding forces on flexible semiconductor films disposed on vapor-releasing adhesives

ABSTRACT

A method comprises providing a handle substrate having a front surface and a back surface; providing a layer of flexible semiconductor material having a front surface and a back surface and an at least partially sacrificial backing layer stack on the back surface of the layer of flexible semiconductor material; bonding the front surface of the layer of flexible semiconductor material to the front surface of the handle substrate; removing at least a portion of the at least partially sacrificial backing layer stack from the back surface of the layer of flexible semiconductor material; opening outgassing paths through the layer of flexible semiconductor material; and processing the layer of flexible semiconductor material.

CROSS REFERENCE

This patent application is a divisional application of U.S. patentapplication Ser. No. 14/795,216, filed Jul. 9, 2015, the disclosure ofwhich is incorporated by reference herein in its entirety.

BACKGROUND

The exemplary embodiments described herein relate generally tosemiconductor devices and methods for the fabrication thereof and, morespecifically, to methods for reducing adhesive debonding forces betweensemiconductor layers and substrates in post-bonding processes.

Optoelectronic devices such as solar cells may incorporate flexiblesemiconductor layers produced by spalling techniques. In these spallingtechniques, a stressor layer is generally used to exfoliate a thin,device-quality, semiconductor layer from a parent semiconductorsubstrate. This process can be repeated multiple times, limited only bythe thickness of the substrate. The thin semiconductor layers (which maybe flexible) can be difficult to handle and process.

In some cases, spalling may involve the temporary bonding of a flexiblesemiconductor layer to a (preferably rigid) low-cost handle substrateand subsequent separation of the flexible semiconductor layer from thehandle substrate using ultraviolet (UV) releasable tape or polyimidereleasable tape. In such spalling techniques, the bonding method shouldbe compatible with semiconductor layer/handle substrate processing attemperatures as high as 200 to 400 degrees C. The bonding temperature islimited by the maximum temperature which can be handled by the tape(maximum temperature of about 90 degrees C. for UV tape and about 200degrees C. for polyimide tape) contacting the stressor layer used forspalling.

Bonding using an epoxy adhesive is one type of bonding method. However,post-bonding processes at temperatures higher than the curingtemperature of the epoxy may lead to both blister formation and adhesionfailure between the impermeable flexible film and the epoxy, an effectattributed to epoxy outgassing.

BRIEF SUMMARY

In one exemplary aspect, a method comprises providing a handle substratehaving a front surface and a back surface; providing a layer of flexiblesemiconductor material having a front surface and a back surface and anat least partially sacrificial backing layer stack on the back surfaceof the layer of flexible semiconductor material; bonding the frontsurface of the layer of flexible semiconductor material to the frontsurface of the handle substrate; removing at least a portion of the atleast partially sacrificial backing layer stack from the back surface ofthe layer of flexible semiconductor material; opening outgassing pathsthrough the layer of flexible semiconductor material; and processing thelayer of flexible semiconductor material.

In another exemplary aspect, a method comprises providing an at leastpartially sacrificial backing layer stack on a back surface of asemiconductor layer; disposing a metal adhesion layer on a front surfaceof the semiconductor layer; bonding the metal adhesion layer to a frontsurface of a substrate; removing at least a portion of the at leastpartially sacrificial backing layer stack from the back surface of thesemiconductor layer; opening outgassing paths through the semiconductorlayer; and processing the semiconductor layer.

In another exemplary aspect, a method comprises providing a stressorlayer stack on a back surface of a semiconductor substrate; adhesivelybonding a front surface of the semiconductor substrate to a handlesubstrate using an epoxy adhesive; removing at least a portion of thestressor layer stack from the back surface of the semiconductorsubstrate; applying a hardmask to the back surface of the semiconductorsubstrate exposed by removing the at least a portion of the stressorlayer stack; forming semiconductor cells in the semiconductor substrateunder the hardmask such that the formed semiconductor cells are spacedapart from each other; and allowing the epoxy adhesive to outgas fromthe spaces defined between the semiconductor cells.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing and other aspects of exemplary embodiments are made moreevident in the following Detailed Description, when read in conjunctionwith the attached Drawing Figures, wherein:

FIGS. 1A through 1D are schematic representations of exemplary methodsof bonding a flexible semiconductor to a rigid substrate using an epoxyadhesive;

FIGS. 1E and 1F are schematic representations of exemplary debondingforces on flexible semiconductors bonded to rigid substrates using theepoxy adhesive due to outgassing;

FIGS. 2A through 2D are schematic representations of exemplary methodsof bonding a flexible semiconductor to a rigid substrate using an epoxyadhesive;

FIG. 2E is a schematic representation of an exemplary method of exposingthe epoxy adhesive of FIGS. 2A through 2D to air prior to heating;

FIGS. 3A through 3E are schematic representations of exemplary methodsof forming and bonding a flexible semiconductor layer to a rigidsubstrate using an epoxy adhesive;

FIGS. 3F and 3G are schematic representations of exposing regions of theepoxy adhesive to air by forming and isolating cells in the flexiblesemiconductor device of FIGS. 3A through 3E using a masking material;

FIG. 3H is a schematic representation of the isolated cells of FIG. 3Gwith the masking material removed;

FIG. 3I is a schematic representation of the isolated cells of FIG. 3Gwith the masking material removed and a portion of the epoxy adhesiveremoved;

FIG. 4A is a photograph of the bonded silicon material of FIG. 3H beforeannealing;

FIG. 4B is a photograph of the bonded silicon material of FIG. 3H afterannealing showing blistering;

FIG. 4C is a photograph of the patterned silicon material of FIG. 3Ibefore annealing;

FIG. 4D is a photograph of the patterned silicon material of FIG. 3Iafter annealing showing the absence of blisters;

FIG. 5 is a simplified block diagram of exemplary electronic devicesthat are suitable for use in the fabrication of flexible semiconductorlayers and devices on flexible carriers; and

FIG. 6 is a logic flow diagram that illustrates the operation of anexemplary method, and a result of execution of computer programinstructions embodied on a computer readable memory, in accordance withan exemplary embodiment of the methods for reducing adhesive debondingforces disclosed herein.

DETAILED DESCRIPTION

Exemplary embodiments of methods for reducing adhesive debonding forcesbetween semiconductor layers and substrates in post-bonding processesare disclosed herein. Such methods include, but are not limited to, theuse of temporary bonding layers comprising epoxies in conjunction withrelease and/or adhesion layers and spalling techniques. Such methodsalso include, but are not limited to, removing selective regions ofsemiconductor layers (and any ancillary layers) to form vent openingsfor adhesive outgassing. However, it should be understood that thedisclosed embodiments are merely illustrative of the claimed methods andthat such methods may be embodied in various forms. The methodsdisclosed herein may be embodied in many different forms and should notbe construed as limited to the exemplary embodiments set forth herein.

The spalling techniques used to form the flexible semiconductor layerson the flexible carriers (described in U.S. Patent ApplicationPublication No. 2010/0311250 A1 to Bedell et al.) allow for controlledremoval of relatively thin layers of semiconductor materials forming thesemiconductor layers from rigid handle substrates to which thesemiconductor layers are transferred.

Referring to FIGS. 1A through 1D, one exemplary method of forming aflexible semiconductor layer on a flexible carrier is shown generally at100 and is hereinafter referred to as “method 100.” As shown in FIG. 1A,a preformed spalled structure is provided, the structure comprisingspall-inducing stressor layer stack 110 on a layer of flexiblesemiconductor material 130. The stressor layer stack 110 may comprise anadhesion layer 115 of titanium (on the flexible semiconductor material130), a seed layer 116 of nickel on the adhesion layer 115, a stressorlayer 120 of nickel deposited onto the seed layer 116, and anultraviolet (UV) releasable transfer tape 125 applied to the stressorlayer 120 to induce the spalling. The flexible semiconductor material130 has an exposed front surface and a back surface to which thestressor layer stack 110 is bonded. The flexible semiconductor material130 may be, for example, a 100-oriented silicon material forming asubstrate or any material selected from the group consisting of silicon,germanium, SiGe, bulk III-V materials, any of the foregoing materialsfurther including epitaxially grown semiconductor layers, any of theforegoing materials further including doped layers, metallic layers,and/or passivating layers, and combinations of the foregoing. Methods bywhich the adhesion layer 115 is deposited on the flexible semiconductormaterial 130 and the seed layer 116 is deposited on the adhesion layer115 include, but are not limited to, thermal evaporation or sputtering.

An epoxy adhesive 135 is disposed on a rigid handle substrate 140.

As shown in FIG. 1B, an optional metal adhesion layer (shown at 150) maybe formed on the exposed front surface of the flexible semiconductormaterial 130. In embodiments employing the metal adhesion layer 150, theflexible semiconductor material 130 with the metal adhesion layer 150 isinterfacially engaged with the epoxy adhesive 135 on the rigid handlesubstrate 140 to bond the flexible semiconductor material 130 to therigid handle substrate 140. When the flexible semiconductor material 130comprises a silicon or silicon oxide-containing semiconductor material,the metal adhesion layer 150 comprises aluminum. However, while aluminumon a native silicon oxide-containing semiconductor material provides asuitable metal adhesion layer 150, other materials (alone or incombination with aluminum) may be used as well. For example, carbon orhydrocarbon contamination may be introduced to the silicon surface priorto the aluminum deposition. Suitable methods for depositing the aluminummetal adhesion layer 150 onto the flexible semiconductor material 130include, but are not limited to, thermal evaporation or sputtering. Inembodiments not employing the metal adhesion layer 150, the flexiblesemiconductor material 130 is bonded directly to the rigid handlesubstrate 140.

As shown in FIG. 1C, pressure is applied to one or both of the stressorlayer stack 110 and the rigid handle substrate 140 such that the epoxyadhesive 135 is substantially uniformly distributed between the metaladhesion layer 150 and the rigid handle substrate 140. The epoxyadhesive is then typically cured at a temperature of from about 40° C.to about 150° C. for a period of time between about 0.1 hours to about 5hours. The tape 125 is removed from the stressor layer stack 110 afterthe curing step.

As shown in FIG. 1D, the adhesion layer 115, the seed layer 116, and thestressor layer 120 are removed from the flexible semiconductor material130. Post-bonding processing steps may be performed on the flexiblesemiconductor material 130. Such post-bonding processing steps include,but are not limited to, patterning, thermal treatments, filmdepositions, and the like. Such post-bonding processing steps may becarried out at temperatures of about 150° C. to about 400° C., which aregenerally higher than the curing temperature of the epoxy adhesive 135.

As shown in FIG. 1E, upon carrying out the post-bonding processes,outgassing of the epoxy adhesive 135 occurs, thereby forming bubbles 143between the layer of epoxy adhesive 135 and the metal adhesion layer150. Such bubbles 143 cause dimples 149 or other discontinuities in theexposed surface of the flexible semiconductor material 130.

As shown in FIG. 1F, the outgassing of the epoxy adhesive 135 may occurthrough the metal adhesion layer 150 to cause the bubble 143 to form atthe underside of the flexible semiconductor material 130. Such bubbles143 cause dimples 149 or other discontinuities in the exposed surface ofthe flexible semiconductor material 130.

Referring now to FIGS. 2A through 2D, another exemplary method offorming a flexible semiconductor layer on a flexible carrier is showngenerally at 200 and is hereinafter referred to as “method 200.” Asshown in FIG. 2A, a preformed spalled structure is provided, thestructure comprising a spall-inducing stressor layer stack 210 on alayer of flexible semiconductor material 230. The stressor layer stack210 may comprise an adhesion layer 215 of titanium (on the flexiblesemiconductor material 230), a seed layer 216 of nickel on the adhesionlayer 215, a stressor layer 220 of nickel deposited onto the seed layer216, and an ultraviolet (UV) releasable transfer tape 225 applied to thestressor layer 120 to induce the spalling. The flexible semiconductormaterial 230 (which may be the same as or similar to that as describedabove) has an exposed front surface and a back surface to which thestressor layer stack 210 is bonded. Methods by which the adhesion layer215 is deposited on the flexible semiconductor material 230 and the seedlayer 216 is deposited on the adhesion layer 215 include, but are notlimited to, thermal evaporation or sputtering.

An epoxy adhesive 235 is disposed on a rigid handle substrate 240.

As shown in FIG. 2B, an optional metal adhesion layer (shown at 250) maybe formed on the exposed front surface of the flexible semiconductormaterial 230. In embodiments employing the metal adhesion layer 250, theflexible semiconductor material 230 with the metal adhesion layer 250 isinterfacially engaged with the epoxy adhesive 235 on the rigid handlesubstrate 240 to bond the flexible semiconductor material 230 to therigid handle substrate 240. When the flexible semiconductor material 230comprises a silicon or silicon oxide-containing semiconductor material,the metal adhesion layer 250 comprises aluminum. However, while aluminumon a native silicon oxide-containing semiconductor material provides asuitable metal adhesion layer 250, other materials (alone or incombination with aluminum) may be used as well. For example, carbon orhydrocarbon contamination may be introduced to the silicon surface priorto the aluminum deposition. Suitable methods for depositing the aluminummetal adhesion layer 250 onto the flexible semiconductor material 230include, but are not limited to, thermal evaporation or sputtering. Inembodiments not employing the metal adhesion layer 250, the flexiblesemiconductor material is bonded directly to the rigid handle substrate240.

As shown in FIG. 2C, pressure is applied to one or both of the stressorlayer stack 210 and the rigid handle substrate 240 such that the epoxyadhesive 235 is substantially uniformly distributed between the metaladhesion layer 250 and the rigid handle substrate 240. The epoxyadhesive is then typically cured at a temperature of from about 40° C.to about 150° C. for a period of time between about 0.1 hours to about 5hours. The transfer tape 225 is removed from the stressor layer stack210.

As shown in FIG. 2D, the adhesion layer 215, the seed layer 216, and thestressor layer 220 are removed from the flexible semiconductor material230. Post-bonding processing steps may be performed on the flexiblesemiconductor material 230. Such post-bonding processing steps include,but are not limited to, patterning, thermal treatments, filmdepositions, and the like. Such post-bonding processing steps may becarried out at temperatures of about 150° C. to about 400° C., which aregenerally higher than the curing temperature of the epoxy adhesive 235.

As shown in FIG. 2E, selected regions of the flexible semiconductormaterial 230 and the metal adhesion layer 250 are removed to form ventopenings 255 to allow the epoxy adhesive 235 to outgas. Means by whichthe selected regions of the flexible semiconductor material 230 and themetal adhesion layer 250 may be removed include, but are not limited to,lithography, chemical etching, dry etching, laser ablation, andcombinations of the foregoing. As can be seen in FIG. 2E, after removingportions of the flexible semiconductor material 230 and the metaladhesion layer 250, portions of the epoxy adhesive 235 may also beremoved, thereby leaving portions of the rigid handle substrate 240exposed. Both (i) optical lithography followed by chemical etching ofthe flexible semiconductor material 230 and the metal adhesion layer 250as well as (ii) laser ablation processes have been found to be suitablemethods for allowing the epoxy adhesive to outgas with regard tostructures in which the flexible semiconductor material 230 comprises aflexible silicon semiconductor.

Referring now to FIGS. 3A through 3G, another exemplary method offorming a flexible semiconductor layer on a flexible carrier layer isshown generally at 300 and is hereinafter referred to as “method 300.”As shown in FIG. 3A, a spall-inducing stressor layer stack 310 isdeposited on a layer of semiconductor material 330. The stressor layerstack 310 may comprise an adhesion layer 315 of titanium (deposited onthe semiconductor material 330), a seed layer 316 of nickel on theadhesion layer 315, a stressor layer 320 of nickel deposited onto theseed layer 316, and an ultraviolet (UV) releasable transfer tape 325applied to the stressor layer 320 to induce the spalling. Thesemiconductor material 330 (which may be the same as or similar to thatas described above) has an exposed front surface and a back surface towhich the stressor layer stack 310 is deposited. Methods by which theadhesion layer 315 is deposited on the semiconductor material 330 andthe seed layer 316 is deposited on the adhesion layer 315 include, butare not limited to, thermal evaporation or sputtering.

The process of controlled spalling separates semiconductor material 330at a plane 333 extending longitudinally through the semiconductormaterial 330 parallel to the adhesion layer 315. Separation of thesemiconductor material 330 may be facilitated by mechanically guidingthe ultraviolet (UV) releasable transfer tape 325 to induce and sustainspalling mode fracture. Separation along plane 333 results in thesemiconductor material 330 having reduced thickness T as shown in FIG.3B, making the thinner semiconductor material, now shown at 330′, haveincreased flexibility. The lower portion of the semiconductor material(shown at 331) may be discarded or recycled.

As shown in FIG. 3C, an optional metal adhesion layer (shown at 350) maybe formed on the exposed front surface of the now flexible semiconductormaterial 330′ after the spalling. In embodiments employing the metaladhesion layer 330, the flexible semiconductor material 330′ with themetal adhesion layer 350 is interfacially engaged with the epoxyadhesive 335 on the rigid handle substrate 340 to bond the flexiblesemiconductor material 330′ to the rigid handle substrate 340. When theflexible semiconductor material 330′ comprises a silicon or siliconoxide-containing semiconductor material, the metal adhesion layer 350comprises aluminum. However, while aluminum on a native siliconoxide-containing semiconductor material provides a suitable metaladhesion layer 350, other materials (alone or in combination withaluminum) may be used as well. For example, carbon or hydrocarboncontamination may be introduced to the silicon surface prior to thealuminum deposition. Suitable methods for depositing the aluminum metaladhesion layer 350 onto the flexible semiconductor material 330′include, but are not limited to, thermal evaporation or sputtering. Inembodiments not employing the metal adhesion layer 350, the flexiblesemiconductor material is bonded directly to the rigid handle substrate340.

As shown in FIG. 3D, pressure is applied to one or both of the stressorlayer stack 310 and the rigid handle substrate 340 such that the epoxyadhesive 335 is substantially uniformly distributed between the metaladhesion layer 350 and the rigid handle substrate 340. The epoxyadhesive is then typically cured at a temperature of from about 40° C.to about 150° C. for a period of time between about 0.1 to about 5hours. The transfer tape 325 is removed from the stressor layer stack310.

As shown in FIG. 3E, the adhesion layer 315, the seed layer 316, and thestressor layer 320 are removed from the flexible semiconductor material330′. Post-bonding processing steps may be performed on the flexiblesemiconductor material 330. Such post-bonding processing steps include,but are not limited to, patterning, thermal treatments, filmdepositions, and the like. Such post-bonding processing steps may becarried out at temperatures of about 150° C. to about 400° C., which aregenerally higher than the curing temperature of the epoxy adhesive 335.

As shown in FIG. 3F, processing can be provided to include cellisolation (if desired). In one exemplary embodiment of isolating cellsin the flexible semiconductor material 330′, a hardmask 370 is depositedas a blanket layer on the flexible semiconductor material 330 and ispatterned and etched through a photoresist (PR) mask. In anotherexemplary embodiment of isolating cells also using a patterned hardmask,hardmask material is deposited through a shadow mask. In eitherembodiment, the hardmask deposition may occur as shown and describedhere or prior to the application of the stressor layer stack 310. In yetanother exemplary embodiment of isolating cells, laser scribing of theflexible semiconductor material 330′ may be carried out.

As shown in FIG. 3G, the cells (shown at 380) are isolated from eachother and supported by the epoxy adhesive 335.

As shown in FIG. 3H, one exemplary method of processing the cells 380 isillustrated. In such a method of processing, the hardmask 370 is removed(e.g., by etching). Portions of the epoxy adhesive 335 between cells 380are also removed by, for example, organic solvents such as ketones,alcohols, or hexanes, dry etching, or laser ablation. Removal of theepoxy adhesive 335 from between the cells 380 allows for the outgassingof the epoxy adhesive 335 under the cells 380.

As shown in FIG. 3I, the portions of the epoxy adhesive 335 between thecells 380 may be maintained in place. Outgassing of the exposed epoxyadhesive 335 may occur.

As shown in FIGS. 4A through 4D, images of the flexible semiconductormaterial 330′ corresponding to those of FIGS. 3H and 3I are shown. InFIG. 4A, a top view image of the (silicon) flexible semiconductormaterial 330′ with the hardmask 370 removed and portions of the epoxyadhesive 335 between the cells 380 also removed is shown at 410. In FIG.4B, the same (silicon) flexible semiconductor material 330 is shown at415 after annealing at 300 degrees C. In FIG. 4C, a top view image ofthe (silicon) flexible semiconductor material 330′ with the hardmask 370removed and retaining the portions of the epoxy adhesive 335 between thecells 380 is shown at 420. In FIG. 4D, this (silicon) flexiblesemiconductor material 330′ is shown at 425 after annealing at 320degrees C.

As shown in FIG. 5, a simplified block diagram of various electronicdevices and apparatuses that are suitable for use in practicing theexemplary embodiments described herein is shown. For example, a computer510 may be used to control one or more of the fabrication processes asdescribed above. The computer 510 includes a controller, such as acomputer or a data processor (DP) 514 and a computer-readable memorymedium embodied as a memory (MEM) 516 that stores a program of computerinstructions (PROG) 518.

The PROG 518 includes program instructions that, when executed by theassociated DP 514, enable the various electronic devices and apparatusto operate in accordance with exemplary embodiments. That is, variousexemplary embodiments may be implemented at least in part by computersoftware executable by the DP 514 of the computer 510, or by hardware,or by a combination of software and hardware (and firmware).

The computer 510 may also include dedicated processors, for exampleflexible semiconductor modeling processor 515.

The computer readable MEM 516 may be of any type suitable to the localtechnical environment and may be implemented using any suitable datastorage technology, such as semiconductor based memory devices, flashmemory, magnetic memory devices and systems, optical memory devices andsystems, fixed memory, and removable memory. The DP 514 may be of anytype suitable to the local technical environment, and may include one ormore of general purpose computers, special purpose computers,microprocessors, digital signal processors (DSPs), and processors basedon a multicore processor architecture, as non-limiting examples.

The exemplary embodiments, as discussed herein and as particularlydescribed with respect to exemplary methods, may be implemented inconjunction with a program storage device (e.g., at least one memory)readable by a machine, tangibly embodying a program of instructions(e.g., a program or computer program) executable by the machine forperforming operations. The operations comprise utilizing the exemplaryembodiments of the method.

Based on the foregoing it should be apparent that various exemplaryembodiments provide a method to fabricate flexible semiconductor layersand devices on flexible carriers.

FIG. 6 is a logic flow diagram that illustrates the operation of amethod 600 (and a result of an execution of computer programinstructions (such as PROG 518)), in accordance with the exemplaryembodiments. In accordance with these exemplary embodiments, a preformedspalled structure is provided, the structure comprising a stressor layerstack formed on a back surface of a semiconductor substrate at block610. An optional metal adhesion layer may be subsequently formed on anexposed front surface of the spalled semiconductor substrate at block620. At block 630, the metal adhesion layer is then adhesively bonded toa rigid handle substrate using an epoxy. If the metal adhesion layer isnot used, the exposed front surface of the semiconductor substrate isbonded to the rigid handle substrate using the epoxy. At least a portionof the stressor layer stack is removed from the back surface of thesemiconductor substrate at block 640. At block 650, a hardmask isapplied to the exposed back surface of the semiconductor substrate. Atblock 660, cells are formed under the hardmask by removing portions ofthe semiconductor substrate and the metal adhesion layer (if present).Portions of the epoxy adhesive not underneath the cells may also beremoved. At block 670, outgassing of the epoxy adhesive occurs.

The various blocks of method 600 shown in FIG. 6 may be viewed as methodsteps, and/or as operations that result from operation of computerprogram code, and/or as a plurality of coupled logic circuit elementsconstructed to carry out the associated function(s).

Example

In one example of a method of reducing adhesive debonding forces betweensemiconductor layers and substrates in post-bonding processes asdescribed in FIGS. 3A through 3I, a preformed spalled structure isprovided, the structure comprising a spall-inducing stressor layer stack310 was on a 100-oriented silicon (Si) substrate (flexible semiconductormaterial 330). The stressor layer stack 310 comprised an adhesion layer315 of titanium (Ti) (150 nm) and a seed layer 316 of nickel (Ni) (400nm), both deposited by sputtering, and a stressor layer 320 ofelectroplated Ni with a thickness of 5 um on top of the Ni seed layer316. The Ni was electroplated on a 2 inch diameter area of the Sisubstrate. A UV releasable tape 325 was then applied to the Ni stressorlayer 320 to induce the spalling. After the Si film was spalled, a 300nm aluminum (Al) metal adhesion layer 350 was thermally evaporated onthe spalled Si surface. The Al side of the resulting flexible filmassembly (tape/stressor layer/Si/Al) was bonded with epoxy adhesive 335to a rigid handle substrate 340 which had also been coated with 300 nmof thermally evaporated Al. This metal layer provided a good adhesionwith the epoxy adhesive 335. The epoxy adhesive 335 used was anelectrically conductive silver filled epoxy (Ablebond 2030SC®, availablefrom Henkel North America). A pressure was applied during the curingprocess by applying a weight on the top of the sample. The curingtemperature was 80 degrees C., with a curing time of 1 hour 15 minutes.

After the curing process was finished, the UV releasable tape 325 wasremoved by exposure to UV light. The Ni stressor layer 320 and the Tiadhesion layer 315 were removed with selective chemical etchants. A hardmask material (Al was used, although other materials were also suitablefor use) was deposited on the exposed semiconductor surface through ashadow mask. The Si was then etched using a reactive ion etching (RIE)process followed by removal of the exposed Al to expose the underlyingepoxy adhesive 335. The sample was then heated to 320 degrees C. Noblistering or adhesion failure between the Si film and the epoxyadhesive 335 was seen, as shown in FIG. 4B.

The experiment was repeated using a laser scribing process. A gridpattern comprising two orthogonal sets of parallel lines spaced apart byabout 10 mm was formed by pulsed laser scribing in an OpTek laserscribing system (available from OpTek Systems Inc., Greenville, S.C.,USA) with a stationary laser and moving sample stage using adiode-pumped Q-switched laser (Nd-YVO4, available from Coherent, Inc.,Santa Clara, Calif., USA) with output at 532 nm (Matrix 532-8-100, alsoavailable from Coherent). The laser had a repetition rate of 60 kHz witha 20 ns pulse width. At the conditions used for scribing (z=1.2 mm focusand 85/35 power/attenuation), the laser pulses had a diameter of about50 um and a pulse energy of about 95 uJ, corresponding to a fluence perpulse of about 4 J/cm² and a peak power density of 2e8 W/cm², and anaverage power of 5.7 W. At the 20 mm/sec scan rate used, each positionalong the scribed line was exposed to about 150 laser pulses (=beamsize*rep rate/scan rate). After laser scribing, the sample was placed inan oven and the temperature was raised to 300 degrees C. with a step of20 C degrees every 5 minutes. No blistering was observed for thissample. Different photographs of the sample corresponding to the FIGS.3H and 3I before and after annealing at 300 degrees C. are shown inFIGS. 4A through 4D.

In one exemplary embodiment, a method comprises providing a handlesubstrate having a front surface and a back surface; providing a layerof flexible semiconductor material having a front surface and a backsurface and an at least partially sacrificial backing layer stack on theback surface of the layer of flexible semiconductor material; bondingthe front surface of the layer of flexible semiconductor material to thefront surface of the handle substrate; removing at least a portion ofthe at least partially sacrificial backing layer stack from the backsurface of the layer of flexible semiconductor material; openingoutgassing paths through the layer of flexible semiconductor material;and processing the layer of flexible semiconductor material.

The method may further comprise disposing a metal adhesion layer on thefront surface of the layer of flexible semiconductor material such thatthe front surface of the layer of flexible semiconductor material isbonded to the front surface of the handle substrate via the metaladhesion layer. The method may further comprise opening the outgassingpaths through the metal adhesion layer. The layer of flexiblesemiconductor material may comprise silicon and the metal adhesion layermay be a thermally evaporated metal layer. The thermally evaporatedmetal layer may be aluminum. Bonding the front surface of the layer offlexible semiconductor material to the front surface of the handlesubstrate may comprise applying an epoxy adhesive to at least a portionof the front surface of the handle substrate. The method may furthercomprise applying pressure to distribute the epoxy adhesive between thelayer of flexible semiconductor material and the handle substrate. Thelayer of flexible semiconductor material may comprise material selectedfrom the group consisting of silicon, germanium, SiGe, bulk III-Vmaterials, epitaxially grown semiconductor layers, any of the foregoingmaterials having doped layers, any of the foregoing materials havingmetallic layers, any of the foregoing materials having passivatinglayers, and combinations of the foregoing materials. The at leastpartially sacrificial backing layer stack may comprise an adhesion layerdisposed on the back surface of the layer of flexible semiconductormaterial, a seed layer disposed on the adhesion layer, a stressor layerdisposed on the seed layer, and a transfer tape disposed on the stressorlayer. Processing the layer of flexible semiconductor material maycomprise at least one of patterning, thermally treating, and depositinga film on the layer of flexible semiconductor material.

In another exemplary embodiment, a method comprises providing an atleast partially sacrificial backing layer stack on a back surface of asemiconductor layer; disposing a metal adhesion layer on a front surfaceof the semiconductor layer; bonding the metal adhesion layer to a frontsurface of a substrate; removing at least a portion of the at leastpartially sacrificial backing layer stack from the back surface of thesemiconductor layer; opening outgassing paths through the semiconductorlayer; and processing the semiconductor layer.

In the method, bonding the metal adhesion layer to the front surface ofthe substrate may comprise applying an epoxy adhesive to at least aportion of the front surface of the substrate. The method may furthercomprise applying pressure to distribute the epoxy adhesive between thefront surface of the substrate and the metal adhesion layer. Thesemiconductor layer may comprise material selected from the groupconsisting of silicon, germanium, SiGe, bulk III-V materials,epitaxially grown semiconductor layers, any of the foregoing materialshaving doped layers, any of the foregoing materials having metalliclayers, any of the foregoing materials having passivating layers, andcombinations of the foregoing materials. The semiconductor layer maycomprise silicon and the metal adhesion layer may be a thermallyevaporated metal layer.

In another exemplary embodiment, a method comprises providing a stressorlayer stack on a back surface of a semiconductor substrate; adhesivelybonding a front surface of the semiconductor substrate to a handlesubstrate using an epoxy adhesive; removing at least a portion of thestressor layer stack from the back surface of the semiconductorsubstrate; applying a hardmask to the back surface of the semiconductorsubstrate exposed by removing the at least a portion of the stressorlayer stack; forming semiconductor cells in the semiconductor substrateunder the hardmask such that the formed semiconductor cells are spacedapart from each other; and allowing the epoxy adhesive to outgas fromthe spaces defined between the semiconductor cells.

The method may further comprise forming a metal adhesion layer on thefront surface of the semiconductor substrate and adhesively bonding thefront surface of the semiconductor substrate to the handle substrate viathe metal adhesion layer. The method may further comprise allowing theepoxy adhesive to outgas through the metal adhesion layer. Thesemiconductor substrate may comprise silicon and the metal adhesionlayer may be a thermally evaporated metal layer. The thermallyevaporated metal layer may be aluminum.

In the foregoing description, numerous specific details are set forth,such as particular structures, components, materials, dimensions,processing steps, and techniques, in order to provide a thoroughunderstanding of the exemplary embodiments disclosed herein. However, itwill be appreciated by one of ordinary skill of the art that theexemplary embodiments disclosed herein may be practiced without thesespecific details. Additionally, details of well-known structures orprocessing steps may have been omitted or may have not been described inorder to avoid obscuring the presented embodiments. It will beunderstood that when an element as a layer, region, or substrate isreferred to as being “on” or “over” another element, it can be directlyon the other element or intervening elements may also be present. Incontrast, when an element is referred to as being “directly on” or“directly” over another element, there are no intervening elementspresent. It will also be understood that when an element is referred toas being “beneath” or “under” another element, it can be directlybeneath or under the other element, or intervening elements may bepresent. In contrast, when an element is referred to as being “directlybeneath” or “directly under” another element, there are no interveningelements present.

The description of the present invention has been presented for purposesof illustration and description, but is not intended to be exhaustive orlimiting in the form disclosed. Many modifications and variations willbe apparent to those of ordinary skill in the art without departing fromthe scope of the invention. The embodiments were chosen and described inorder to best explain the principles of the invention and the practicalapplications, and to enable others of ordinary skill in the art tounderstand the invention for various embodiments with variousmodifications as are suited to the particular uses contemplated.

The invention claimed is:
 1. A method, comprising: providing a handle substrate having a front surface and a back surface; providing a layer of flexible semiconductor material having a front surface and a back surface and an at least partially sacrificial backing layer stack on the back surface of the layer of flexible semiconductor material; disposing a metal adhesion layer on the front surface of the layer of flexible semiconductor material; bonding the front surface of the layer of flexible semiconductor material with the metal adhesion layer to the front surface of the handle substrate such that the front surface of the layer of flexible semiconductor material is bonded to the front surface of the handle substrate via the metal adhesion layer; removing at least a portion of the at least partially sacrificial backing layer stack from the back surface of the layer of flexible semiconductor material; opening outgassing paths through the layer of flexible semiconductor material; and processing the layer of flexible semiconductor material.
 2. The method of claim 1, further comprising opening the outgassing paths through the metal adhesion layer.
 3. The method of claim 1, wherein the layer of flexible semiconductor material comprises silicon and the metal adhesion layer is a thermally evaporated metal layer.
 4. The method of claim 1, wherein bonding the front surface of the layer of flexible semiconductor material with the metal adhesion layer to the front surface of the handle substrate comprises applying an epoxy adhesive to at least a portion of the front surface of the handle substrate.
 5. The method of claim 4, further comprising applying pressure to distribute the epoxy adhesive between the metal adhesion layer and the front surface of the handle substrate.
 6. The method of claim 1, wherein bonding the front surface of the layer of flexible semiconductor material with the metal adhesion layer to the front surface of the handle substrate comprises applying an epoxy adhesive to at least a portion of the metal adhesion layer.
 7. The method of claim 1, wherein the layer of flexible semiconductor material comprises material selected from the group consisting of silicon, germanium, SiGe, bulk III-V materials, epitaxially grown semiconductor layers, any of the foregoing materials having doped layers, any of the foregoing materials having metallic layers, any of the foregoing materials having passivating layers, and combinations of the foregoing materials.
 8. The method of claim 1, wherein the at least partially sacrificial backing layer stack comprises an adhesion layer disposed on the back surface of the layer of flexible semiconductor material, a seed layer disposed on the adhesion layer, a stressor layer disposed on the seed layer, and a transfer tape disposed on the stressor layer.
 9. The method of claim 1, wherein processing the layer of flexible semiconductor material comprises at least one of patterning, thermally treating, and depositing a film on the layer of flexible semiconductor material.
 10. A method, comprising: providing an at least partially sacrificial backing layer stack on a back surface of a semiconductor layer; disposing a metal adhesion layer on a front surface of the semiconductor layer; bonding the metal adhesion layer to a front surface of a substrate; removing at least a portion of the at least partially sacrificial backing layer stack from the back surface of the semiconductor layer; opening outgassing paths through the semiconductor layer; and processing the semiconductor layer; wherein the at least partially sacrificial backing layer stack comprises an adhesion layer disposed on the back surface of the layer of the semiconductor layer, a seed layer disposed on the metal adhesion layer, a stressor layer disposed on the seed layer, and a transfer tape disposed on the stressor layer.
 11. The method of claim 10, wherein bonding the metal adhesion layer to the front surface of the substrate comprises applying an epoxy adhesive to at least a portion of the front surface of the substrate and causing the epoxy adhesive to engage the metal adhesion layer.
 12. The method of claim 11, further comprising applying pressure to distribute the epoxy adhesive between the front surface of the substrate and the metal adhesion layer.
 13. The method of claim 10, wherein bonding the metal adhesion layer to the front surface of the substrate comprises applying an epoxy adhesive to at least a portion of the metal adhesion layer and causing the epoxy adhesive to engage the front surface of the substrate.
 14. The method of claim 10, wherein the semiconductor layer comprises material selected from the group consisting of silicon, germanium, SiGe, bulk III-V materials, epitaxially grown semiconductor layers, any of the foregoing materials having doped layers, any of the foregoing materials having metallic layers, any of the foregoing materials having passivating layers, and combinations of the foregoing materials.
 15. The method of claim 10, wherein the semiconductor layer comprises silicon and the metal adhesion layer is a thermally evaporated metal layer.
 16. A method, comprising: providing an at least partially sacrificial backing layer stack on a back surface of a semiconductor layer; disposing a metal adhesion layer on a front surface of the semiconductor layer; bonding the metal adhesion layer to a front surface of a substrate; removing at least a portion of the at least partially sacrificial backing layer stack from the back surface of the semiconductor layer; opening outgassing paths through the semiconductor layer; and processing the semiconductor layer; wherein processing the semiconductor layer comprises at least one of patterning, thermally treating, and depositing a film on the semiconductor layer.
 17. The method of claim 16, wherein bonding the metal adhesion layer to the front surface of the substrate comprises applying an epoxy adhesive to at least a portion of the metal adhesion layer and causing the epoxy adhesive to engage the front surface of the substrate.
 18. The method of claim 17, further comprising applying pressure to distribute the epoxy adhesive between the front surface of the substrate and the metal adhesion layer.
 19. The method of claim 16, wherein the semiconductor layer comprises material selected from the group consisting of silicon, germanium, SiGe, bulk III-V materials, epitaxially grown semiconductor layers, any of the foregoing materials having doped layers, any of the foregoing materials having metallic layers, any of the foregoing materials having passivating layers, and combinations of the foregoing materials.
 20. The method of claim 16, wherein the semiconductor layer comprises silicon and the metal adhesion layer is a thermally evaporated metal layer. 